The Chicago Bears are in danger of starting the 1986 campaign on the injured list with writer`s cramp.

Two more local heroes--quarterback Jim McMahon and middle linebacker Mike Singletary--checked into camp with autobiographies.

McMahon and Singletary are among the more interesting personalities on the Super Bowl champions. And they are outspoken--if not in total agreement

--about what it takes to excel in athletics.

At first glance, these two warriors appear to be polar opposites. McMahon, irreverent beer-guzzler in the mold of legendary quarterbacks like Snake Stabler and Bobby Layne; Singletary, fanatical disciplinarian who approaches the gridiron as a moral battlefield.

''I was born to be a hellion,'' admits McMahon. He grew up Irish Catholic in California and Utah caring for sports and little else, except for pranks like sticking thumbtacks ''in the fat rear end of this Hawaiian kid'' during the Pledge of Allegiance.

As for Singletary`s childhood in Houston: ''I spent almost all of my life until the age of 7 in and out of the hospital. Pneumonia, high blood pressure, oxygen tents. . . . Sometimes I was so sick my mom would just look at me and start crying.''

Two brothers were killed in accidents when Mike was a boy. His father, a preacher of mixed blood (German father, black mother), eventually ''moved out, to the other side of town, to a bigger house, to another woman. . . . And when he left my mom would just sit in the kitchen and cry. `Don`t worry Mom,` I would say. `One of these days I`m going to buy you a big new house.` ''

No wonder Singletary accepted a football scholarship at Baylor to play under a coach like Grant Teaff, who spoke so earnestly ''about the importance of believing and winning. Not the winning associated with scoreboards but, rather, the kind that means overcoming odds, taking adversity and body-slamming it to the turf.''

Meanwhile, McMahon was having a dreadful time with the behavior code at

''Disneyland, otherwise known as Brigham Young University . . . an unreal world out there in Provo, Utah. Most of the people are Mormons, and most of them aren`t normal, as I see it.''

Singletary and McMahon both made All-American, both were drafted by the Bears (Singletary in the second round, 1981; McMahon in the first round, 1982), and both matured with the team alongside new coach Mike Ditka.

Singletary on Ditka: ''There was nothing phony about him. You`d see him in his office at 5:30 a.m., jogging the halls, then again at midnight, closing the lights. He wanted to be the best. . . . That was good enough for me.''

McMahon on Ditka: ''He`a a born-again Christian who says he`s very religious, which is fine. But I guess for three hours every Sunday afternoon that doesn`t hold, because some of the words that come out of his mouth when he`s coaching I wouldn`t even use. Some of the words, I never even heard!''

Although both players have had run-ins with Ditka, they admire his dedication as a player and coach. The same respect is not evident for the Bears club president, Michael McCaskey.

Singletary on McCaskey: '' . . . a new-breed of owner who favors blue shirts, red ties, and an uncluttered desk. . . . He is a man who enjoys using words like finite and continuum. And the sound of his own voice.''

McMahon on McCaskey: '' . . . doesn`t have any qualifications to operate the Bears except his name (McCaskey is the grandson of Bears founder George Halas). . . . he was jumping around our locker room, in January of 1986, with a Super Bowl trophy. He must think he`s the reason we won . . . he`d be offended to learn that most of us feel we won in spite of him.''

It`s worth noting that all three of the most recent Bears autobiographers --Ditka, Singletary, and McMahon--have felt slighted by management and hinted that they might eventually seek employment elsewhere.